Improvements in multi-spindle machine tools

ABSTRACT

The present invention provides certain additional improvements for such mechanical-type multi-axis machine tools. These improvements include: (1) permitting the spindles to be rotated about their respective axes relative to the member independently of one another, (2) providing a low-cost, and yet highly-effective, sensor apparatus for determining the angular position of the member relative to the frame without the use of an expensive encoder or the like, (3) mounting the rotatable member more precisely relative to the frame, and (4) providing a zero-backlash tool slide on the frame for imparting an action to a workpiece.

TECHNICAL FIELD

The present invention relates generally to machine tools, and, moreparticularly, to various improvements that can be made tomechanical-type multi-spindle machine tools to improve theirperformance. The improvements are particularly adapted for use with, butare not limited to, Davenport® multi-spindle automatic screw machines.

BACKGROUND ART

An automatic screw machine is a machine tool for machining a widevariety of parts from bar-stock. The bar-stock may have round, square orpolygonal transverse cross-sections, and may be supplied to the screwmachine in axial lengths on the order of ten to twelve feet. The screwmachine typically has a head rotatably mounted on a supporting frame.The head is controllably indexable about the head axis through aplurality of successive angular positions. A plurality ofcircularly-spaced spindle assemblies are mounted on the head forrotation with the head about the head axis, and for rotation relative tothe head about the various individual spindle assembly axes. Lengths ofbar-stock are supplied axially to each spindle assembly, and rotate withthe head assembly about the head axis. Hence, the rotatable head and thebar-stock supplied to the various spindle assemblies somewhat resemblesa Gatling gun in outward appearance. The screw machine is adapted toperform various machining operations on cantilevered lengths ofbar-stock (i.e., workpieces) that are held by and extend beyond thespindle assembly collets at the various angular positions of the head.

Each spindle assembly typically has an outer spindle rotatably mountedon the head, and is elongated along its own individual spindle assemblyaxis. The several spindle assembly axes are parallel to the head axis.Each outer spindle has an inwardly- and forwardly-facing frusto-conicalcam surface. An inner spindle is arranged within the outer spindle forrotation with the outer spindle about the associated spindle assemblyaxis, and is mounted for limited axial movement relative to theassociated outer spindle. A spindle-moving means or mechanism isoperatively arranged to exert a force on the inner spindle tocontrollably move the inner spindle in one axial direction relative tothe outer spindle. A collet is mounted on the inner spindle for movementtherewith. The collet has a plurality of fingers that extend forwardlyfrom a body. These fingers have angularly-segmented outwardly- andrearwardly-facing frusto-conical cam surfaces that engage theinwardly-facing cam surface on the associated outer spindle. Each fingerhas a pad that is adapted to be moved radially inwardly to engage apenetrant portion of the bar-stock when the inner spindle is moved insuch one axial direction relative to the outer spindle. When thespindle-moving mechanism releases the force exerted on the innerspindle, the inner spindle moves in the opposite axial directionrelative to the associated outer spindle, and the collet fingers arepermitted to move radially outwardly (i.e., to spring back) toward theiroriginal positions such that the collet pads will disengage from andrelease the bar-stock.

A feed tube is arranged within each inner spindle for rotation about theassociated spindle assembly axis, and for axial movement relativethereto. The feed tube has a plurality of feed fingers that are adaptedto engage a length of penetrant bar-stock within the feed tube. A feedtube moving means or mechanism is provided for selectively causing thefeed tube and feed fingers to selectively reciprocate in either axialdirection (i.e., forwardly and rearwardly) relative to the innerspindle. Such movement of the feed tube is coordinated with operation ofthe collet so that the feed fingers may advance the bar-stock forwardlytoward and through the collet when the collet fingers have movedradially away from the workpiece such that the collet is open. When thecollet is closed, the feed tube is moved rearwardly away from thecollet, with the feed fingers sliding along the bar-stock held in theclosed collet.

One particular type of screw machine is the Davenport® five-spindleautomatic screw machine. Davenport® is a registered trademark ofBrinkman Products, Inc., 167 Ames Street, Rochester, N.Y. 14611, and theparent company of Davenport Machine, Inc. of the same address. Theoriginal Davenport® machines were developed in the late 19th Century andearly 20th Century. Many early-version and remanufactured Davenport®machines are still in service today, and brand new machines are beingsold as well.

The basic structure and operation of a Davenport® Model B five-spindlescrew machine is shown and described in videos entitled, “DavenportModel B—Multi-Spindle Screw Machine #1”, available athttps://www.youtube.com/watch?v=N8hBtoNi3El, and “Davenport ModelB—Multi-Spindle Screw Machine #2”, available athttps://www.youtube.com/watch?v=ppQydP2bd4k, the aggregate disclosuresof which are hereby incorporated by reference. An indexing mechanism isadapted to controllably rotate the head relative to the frame throughfive sequential indexing positions (i.e., at 0°, 72°, 144°, 216°, 288°,. . . ) relative to the frame. These machines have a number of cuttingand forming tools mounted on the frame and operatively arranged toengage the cantilevered lengths of bar-stock (i.e., workpieces) held byand extending beyond the collets of the several spindle assemblies ateach of the various angularly-spaced index positions of the head. Asingle motor acted through a gear train, and rotated each of the fivespindle assemblies simultaneously about their own individual spindleassembly axes at the same angular speed. The cutting and forming toolsare mechanically coupled to the motor output shaft, and are timed (viavarious cams and followers) to perform various operations (both axiallyand radially) on the workpieces at each of the head index positions.

Over the years, the performance of these Davenport® machines has beenimproved by the addition of servo control (see, e.g., U.S. Pat. No.6,421,895 B2), by the addition of man-machine interface control (Id.),by improved heads, by high-precision spindle assemblies (see, e.g., U.S.Pat. Nos. 6,817,273 B2 and 7,036,991 B2), by quick-change bearingassemblies (see, e.g., U.S. Pat. No. 7,402,927 B2), by larger spindleassemblies to accommodate oversized bar-stock (see, e.g., U.S. patentapplication Ser. No. 15/087,381, filed Mar. 31, 2016), by the use ofimproved collets (Id.), and the like. Indeed, others have filed patentapplications on their perceived improvements to such Davenport®machines. (See, e.g., U.S. Pat. Nos. 6,000,499 A, 5,356,244 A and5,205,376 A.) The aggregate disclosures of all of these prior artpatents and patent application are hereby incorporated by reference toillustrate pertinent portions of such Davenport® machines and theirrespective specific improvements thereto. Thus, the mechanical-type ofDavenport® five-spindle automatic screw machines have enjoyed a sort ofrenaissance with these various improvements upgrading theircapabilities, accuracy and performance.

Another type of such machine tool is the Penta 518 five-spindle lathe,reportedly manufactured and sold by ZPS America LLC, 4950 West 79thStreet, Indianapolis, Ind. 46268 (www.zpsamerica.com) and Tajmac-ZPS,a.s., Trida 3, kvetna 1180, CZ-76487, Tiln, Malenovice, Czechoslovakia(www.tajmac-zps.cz). The Penta 518 machine is another mechanical-typemulti-spindle machine tool. The Penta 518 machine is shown and describedin an article, “Five-Spindle Lathe Expands CNC Multi Line,” ProductionMachining, Vol. 17, Issue 3 (March 2017).

In recent years, improved CNC screw machines have been developed thatuse digital technology to control the rotation of various spindleassemblies independently of one another, to control the operation ofvarious tools, and to monitor the position of the head relative to theframe by means of expensive encoders. While these CNC machines arecertainly capable, they are expensive to purchase and generally requirespecially-trained operators to program them. Hence, these CNC machinesare particularly suited for long production runs where the higher costof programming and set-up may be spread over a large number of partsproduced. A current CNC machine is also reportedly manufactured and soldby the aforesaid ZPS America and Tajmac-ZPS, a.s. This CNC machine isreported to cost in excess of $800,000.

However, additional improvements can be made to the oldermechanical-type machine tools, such as the Davenport® five-spindle screwmachines, to further enhance their accuracy, performance and servicelife. They are generally faster, more productive and more economicalthan the more-recent CNC machines.

Hence, there is believed to be a continued need for improvements to suchmechanical-type multi-spindle screw machines generally, and theDavenport® multi-axis automatic screw machines in particular, that (1)will permit the spindle assemblies to be rotated about their respectiveaxes relative to the head independently of one another, (2) will providea low-cost, and yet effective, means for determining the angularposition of the head relative to the frame without the use of anexpensive encoder or the like, (3) will mount the head more preciselyrelative to the frame, and (4) will provide zero-backlash tool slides onthe frame for imparting an action to a workpiece.

DISCLOSURE OF THE INVENTION

With reference to the corresponding parts, portions or surfaces of thedisclosed embodiment(s), merely for purposes of illustration and not byway of limitation, the present invention provides several improvementsfor use in a machine tool.

In one aspect, the invention provides an improved multi-spindle machinetool (20), which broadly comprises: a frame (22); a member (21) mountedon the frame for rotation about a member axis (x₁-x₁); an indexingmechanism (25) acting between the frame and member for selectivelycausing the member to rotate about the member axis relative to the framesequentially between a plurality of angularly-spaced index positions; aplurality of spindle assemblies (28) mounted on the member for rotationtherewith, each spindle assembly being mounted for rotation relative tothe member about its own individual spindle assembly axis; a pluralityof motors (29) mounted on the frame; and a plurality of ring gears (30)mounted on the member and engaging a respective one of the spindleassemblies, each ring gear being driven by a respective one of themotors; whereby the motors may be operated independently of one anotherto selectively rotate the respective spindle assemblies relative to themember at the desired rotational speeds.

The ring gears may be spaced axially from one another along the memberaxis.

Each of the motors may have an output shaft and a driving gear mountedon the output shaft, and wherein each driving gear is arranged to rotatea respective one of the ring gears.

The plurality may be five.

The machine tool may be a Davenport® automatic screw machine, and themember may be a head of the screw machine.

The indexing mechanism may be a Geneva indexing mechanism.

In another aspect, the invention provides a machine tool (20), whichbroadly comprises: a frame (22); a member (21) mounted on the frame forrotation about a member axis (x₁-x₁); an indexing mechanism (25) actingbetween the frame and member for selectively causing the member torotate relative to the frame sequentially between a plurality ofangularly-spaced index positions; and a sensor apparatus (40) fordetermining the angular position of the member relative to the frame,the sensor apparatus including: a first plurality of sensors (50, 51,52) mounted on one of the frame and member and arranged to face towardthe other of the frame and member, the sensors being arranged in a firstarray; a second plurality of features (55-61) provided in the other ofthe frame and member at each index position and arranged to face towardthe sensors, the features being arranged in a second array; and means(62) for generating a signal from the sensors such that the signal willindicate the particular index position of the member relative to theframe.

The second plurality may be different from the first plurality at someof the index positions.

The sensors may be proximity sensors operatively arranged to sense thepresence or absence of material across the interface between the frameand member. The features may include at least one hole provided in theother of the frame and member.

The first array may be arranged to face toward the second array when themember is in each index position.

The member may be a head having a plurality of spindle assembliesmounted thereon, wherein the head has a head axis, wherein each spindleassembly has an individual spindle axis, and wherein the spindleassemblies are mounted on the head for rotation with the head about thehead axis and for rotation relative to the head about their respectiveindividual spindle axes.

The machine tool may be a Davenport® automatic screw machine.

In another aspect, the invention provides an improved multi-spindlemachine tool (20), which broadly comprises: a frame (22); a member (21)mounted on the frame for rotation about a member axis (x₁-x₁); anindexing mechanism (25) acting between the frame and member forselectively causing the member to rotate about the member axis relativeto the frame sequentially between a plurality of angularly-spaced indexpositions; a plurality of spindle assemblies (28) mounted on the memberfor rotation therewith, each spindle assembly being mounted for rotationrelative to the member about its own individual spindle assembly axis;and at least one rolling-element (64) bearing acting between the memberand frame such that the position of the member relative to the frame maybe controlled at each of the index positions.

The machine tool may be a Davenport® automatic screw machine, and themember may be head of the screw machine.

In still another aspect, the invention provides an improvedmulti-spindle machine tool (20), which broadly comprises: a frame (22);a member (21) mounted on the frame for rotation about a member axis(x₁-x₁); an indexing mechanism (25) acting between the frame and memberfor causing the member to rotate relative to the frame about the memberaxis sequentially between a plurality of angularly-spaced indexpositions; a plurality of spindle assemblies (28) mounted on the memberfor rotation therewith, each of the spindles being mounted for rotationrelative to the member about its own individual spindle axis; a chuckmounted on each spindle assembly for holding a workpiece; means forcontrollably rotating each of the spindle assemblies independently ofone another at a desired angular speed; a zero-backlash tool slide (65)mounted on the frame and arranged to be controllably moved relative tothe workpiece at each index position; and a tool (72) mounted on theslide for imparting an action to the workpiece (VV).

The tool slide may include a ball screw.

The tool slide may include a linear rail.

The machine tool may be a Davenport® five-spindle automatic screwmachine, and wherein the member may be a head on the screw machine.

Accordingly, the general object of the invention is to provideimprovements to such mechanical-type multi-spindle screw machinesgenerally, and the Davenport® multi-axis automatic screw machines inparticular, that (1) will permit the spindle assemblies to be rotatedabout their respective axes relative to the head independently of oneanother, (2) will provide a low-cost, and yet effective, means fordetermining the angular position of the head relative to the framewithout the use of an expensive encoder or the like, (3) will mount thehead more precisely relative to the frame, and/or (4) will providezero-backlash tool slides on the frame for imparting an action to aworkpiece. These various improvements may be used singly, or incombination with one another.

These and other objects and advantages will become apparent from theforegoing and ongoing written specification, the drawings and theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary front elevational view of a portion of amulti-axis machine tool, and, more particularly, an improved Davenport®five-spindle automatic screw machine, incorporating the improvements ofthe present invention.

FIG. 2 is a fragmentary top plan view of the Davenport® five-spindleautomatic screw machine shown in FIG. 1.

FIG. 3 is a fragmentary vertical sectional view thereof, taken generallyon line 3-3 of FIG. 1.

FIG. 4 is a greatly-enlarged detail view, taken within the indicatedellipse in FIG. 3, of the improved means for mounting a spindle assemblyon the head.

FIG. 5 is a fragmentary side elevation of a portion of the head andindexing mechanism, showing one form of the sensor apparatus mounted ona guard and arranged to interact with features on the driven gear of theindexing apparatus.

FIG. 6 is a fragmentary vertical sectional view thereof, taken generallyon line 6-6 of FIG. 5.

FIG. 7 is a fragmentary side elevation of the improved tool slide.

FIG. 8 is a fragmentary top plan view of the tool side shown in FIG. 7.

FIG. 9 is a fragmentary transverse vertical sectional view thereof,taken generally on line 9-9 of FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

At the outset, it should be clearly understood that like referencenumerals are intended to identify the same structural elements, portionsor surfaces consistently throughout the several drawing figures, as suchelements, portions or surfaces may be further described or explained bythe entire written specification, of which this detailed description isan integral part. Unless otherwise indicated, the drawings are intendedto be read (e.g., cross-hatching, arrangement of parts, proportion,degree, etc.) together with the specification, and are to be considereda portion of the entire written description of this invention. As usedin the following description, the terms “horizontal”, “vertical”,“left”, “right”, “up” and “down”, as well as adjectival and adverbialderivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”,etc.), simply refer to the orientation of the illustrated structure asthe particular drawing figure faces the reader. Similarly, the terms“inwardly” and “outwardly” generally refer to the orientation of asurface relative to its axis of elongation, or axis of rotation, asappropriate.

Referring now to the drawings, the present invention provides certainimprovements in machine tools. In the drawings, the particular type ofmachine tool is depicted as being a Davenport® five-spindle automaticscrew machine. However, it should be clearly understood that theimprovements are not limited to use with such Davenport® machines, butpossess a general applicability to other types of multi-axis machinetools as well. Thus, as used herein, the term “machine tool” is intendedbroadly to refer to a machine for imparting an action to a workpiece,and a “multi-spindle machine tool” is intended to refer to a machinetool having more than one spindle assembly mounted on a “member”(sometimes known as a “head’ or “drum”) that is mounted for rotationalmovement about a member axis relative to a frame. In many cases, anindexing mechanism, such as a Geneva-type mechanism, is operativelyarranged to cause the member to rotate sequentially through a pluralityof angularly-spaced index positions.

As noted above, over the years, certain improvements have been providedfor the mechanical-type multi-axis machine tools in order to increasetheir accuracy and capability. These prior art improvements haveincluded the addition of servo control, by the addition of man-machineinterface control, by improved heads, by high-precision spindleassemblies, by quick-change bearing assemblies, by larger spindleassemblies to accommodate oversized bar-stock, by the use of improvedcollets, and the like.

The present invention provides certain additional improvements for suchmechanical-type multi-axis machine tools. These improvements include:(1) permitting the spindles to be rotated about their respective axesrelative to the member independently of one another, (2) providing alow-cost, and yet highly-effective, sensor apparatus for determining theangular position of the member relative to the frame without the use ofan expensive encoder or the like, (3) mounting the rotatable member moreprecisely relative to the frame, and (4) providing zero-backlash toolslides on the frame for imparting an action to a workpiece. Theseimproved features will be discussed seriatim herebelow.

Independent Spindle Assembly Rotation (FIGS. 1-4)

FIG. 1 is a fragmentary front elevation of a portion of a Davenport®five-spindle automatic screw machine, generally indicated at 20. In thefollowing discussion, detailed descriptions of portions of the screwmachine that are “old” (i.e., part of the prior art) will been omittedin the interest of clarity. This machine is shown as having a member orhead 21 mounted on a frame 22 for rotation about a member axis x₁-x₁. Anindexing mechanism 23, such as a Geneva drive, is arranged to actbetween the frame and head, and is operable to selectively cause thehead to rotate about the head axis x₁-x₁ sequentially between fiveangularly-spaced index positions. The entire indexing mechanism does notappear in FIGS. 1-4, but the driven wheel 24 thereof is shown in FIGS. 5and 6. Geneva-type indexing mechanisms are well known, and have beenused for many years on Davenport® machines.

In FIG. 1, the head 21 is shown as having five circularly-spacedlongitudinally-extending openings, each adapted to receive a spindleassembly. The rotational interval between these index positions is 72°for a five-spindle machine. These five head openings are severallyindicated at 25, and are individually identified by the letters A, B, C,D and E, respectively. The spindle assemblies 26 themselves areindividually “old”, and are more fully shown and described in U.S.patent application Ser. No. 15/087,381, filed Mar. 31, 2016, theaggregate disclosure of which is hereby incorporated by reference.

There are five spindle assembles 26, one for each head opening. Thespindle assemblies are individually identified by the suffixes A-E,respectively. Thus, spindle assembly 26A is operatively arranged in headopening 25A, spindle assembly 26B (not shown) is operatively arranged inhead opening 25B, and so on. In FIG. 4, one such spindle assembly 26A isshown as including, in pertinent part, an outer spindle 28A. The innerspindle, the collet, the feed fingers, the workpiece, and the means foradvancing the workpiece and for operating the collet of each spindleassembly have been omitted to avoid obfuscating the present improvement.Suffice it to say here that each spindle assembly 26 is positionedwithin the associated head opening 25, and is elongated along itsrespective spindle assembly axis. In FIGS. 2 and 4, the spindle assembly26A in the twelve o'clock position of FIGS. 1 and 3 is shown as having aspindle axis x_(A)-x_(A). The other spindle assemblies (not shown) aresimilarly elongated along their respective spindle axes x_(B)-x_(B),x_(C)-x_(C), x_(D)-x_(D) and x_(E)-x_(E), respectively. Each spindleassembly axis is parallel to head axis x₁-x₁. Each spindle assembly ismounted on the head for rotation therewith, and is mounted for rotationrelative to the head about its own individual spindle axis.

In FIG. 1, a plurality of motors, severally indicated at 29 andindividually identified by the suffixes A, B, . . . , E, are shown asbeing mounted on the frame. As best shown in FIG. 4 a plurality of ringgears, severally indicated at 30 and individually identified by thesuffixes A, B, . . . , E, are mounted on the head at variousaxially-spaced locations along the head axis, and are respectivelyarranged to rotate associated ones of the spindle assemblies 26 viasynchronous belts, severally indicated at 31 and again individuallyidentified by the suffixes A, B, . . . , E, respectively. FIG. 4 depictsring gear 30A as being coupled to outer spindle 26A via an intermediategears 32A. Ring gears 30B, 30C, 30D and 30E are similarly coupled totheir respective outer spindles 26B, 26C, 26D and 26E (not shown) viasimilar intermediate gears 32B, 32C, 32D and 32E (not shown),respectively. Thus, motor 29A is arranged to rotate spindle assembly 26Avia synchronous belt 31A, ring gear 30A and intermediate gear 32A, motor29B is arranged to rotate spindle assembly 29B via synchronous belt 31B,ring gear 30B and intermediate gear 32B, motor 29C is arranged to rotatespindle assembly 29C via synchronous belt 31C, ring gear 30C andintermediate gear 32C, motor 29D is arranged to rotate spindle assembly29D via synchronous belt 31D, ring gear 30D and intermediate gear 32D,and motor 29E is arranged to rotate spindle assembly 29E via synchronousbelt 31E, ring gear 30E and intermediate gear 32E.

In FIG. 4, each of the ring gears 30A, 30B, . . . , 30E is rotatablymounted on the head via roller bearings 33A, 33B, . . . , 33E,respectively. These several intermediate gears may have their innersurfaces secured to the outer spindle 28 of the associated spindleassembly, and may have their outer surfaces in meshing engagement withthe inner surfaces of the associated ring.

The spindle assembly may be mounted on the head by high-precisionbearing assemblies, such as shown and described in U.S. Pat. Nos.6,817,273 B2 and/or 7,036,991 B2.

Motors 29 may be servomotors, stepping motors, or the like. The variousmotors may be operated independently of one another to selectivelyrotate the respective associated spindle assemblies relative to the headat the desired rotational speeds so as to controllably vary therotational speeds of the workpieces held at each of the index positions.In addition, this improvement offers the capability of stopping,reversing and orienting the workpiece in the midst of an operation ateach index position.

Thus this first aspect broadly provides a multi-spindle machine tool 20,comprising: a frame 21; a member 22 mounted on the frame for rotationabout a member axis x₁-x₁; an indexing mechanism 23 acting between theframe and member for selectively causing the member to rotate about themember axis relative to the frame sequentially between a plurality ofangularly-spaced index positions; a plurality of spindle assemblies 26A,26B, . . . , 26E mounted on the member for rotation therewith, eachspindle assembly being mounted for rotation relative to the member aboutits own individual spindle assembly axis x_(A)-x_(A), x_(B)-x_(B),x_(E)-x_(E); a plurality of motors 29A, 29B, . . . , 29E mounted on theframe; and a plurality of ring gears 30A, 30B, . . . , 30E mounted onthe member and engaging a respective one of the spindle assemblies 26A,26B, . . . , 26E, each ring gear being driven by a respective one of themotors; whereby the motors may be operated independently of one anotherto selectively rotate the respective spindle assemblies relative to themember at the desired angular speeds.

Head Position Sensor (FIGS. 5-6)

Referring now to FIGS. 5-6, the driven wheel 24 of a Geneva-typeindexing mechanism 23 is shown as having an outer toothed portion 36 inmeshing engagement with a toothed portion 38 on the head. Driven wheel24 has a plurality of blind slots extending radially inwardly fromvarious circumferentially-spaced locations on its outer surface. Theseblind slots are adapted to receive the pin (not shown) mounted on thedriving wheel (not shown) of the Geneva mechanism. In the well-knownmanner, rotation of the Geneva driving wheel causes the Geneva drivenwheel to rotate about its axis x₂-x₂ between five successive angularindex positons spaced 72° apart. This, in turn, causes like indexingmotion of head 21.

An arcuate guard 39 is mounted on the frame 22, and closely encircles aportion of the Geneva driven wheel 24. A sensor apparatus, generallyindicated at 49, comprises three proximity sensors 50, 51, 52 mounted onthe guard and having their sensing heads arranged to closely facecooperative features on the Geneva driven wheel. In the illustratedembodiment, these features are different patterns of holes drilled atinto the driven wheel at each of the five index positions.

When head opening 25A is in the 12:00 o'clock position (as seen in FIG.6), proximity sensors 50 and 51 are radially aligned with blind holes53, 54 drilled into the driven wheel. However, proximity sensor 52 isnot aligned with any hole, and senses the presence of a proximateportion of the adjacent driven wheel.

When the indexing mechanism is operated to move head opening 25B to the12:00 o'clock positon (as seen in FIG. 6), proximity sensor 51 will bealigned with a blind hole 55 drilled into the driven wheel. However,proximity sensors 50, 52 will not be aligned with any hole, and willsense the presence of proximate portions of the adjacent driven wheel.

When the indexing mechanism is operated to move head opening 25C to the12:00 o'clock position (as seen in FIG. 6), proximity sensor 50 will notbe aligned with any hole, and will sense the presence of a proximateportion of the adjacent driven wheel. However, proximity sensors 51, 52will be aligned with blind holes 56, 58, respectively, drilled into thedriven wheel.

When the indexing mechanism is operated to move head opening 25D to the12:00 o'clock position (as seen in FIG. 6), proximity sensors 50, 52will be aligned with blind holes 59, 60, respectively, drilled in thedriven wheel. However, proximity sensor 51 will not be aligned with anyhole, and will sense the presence of a proximate portion of the adjacentdriven wheel.

When the indexing mechanism is operated to move head opening 25E to the12:00 o'clock position (as shown in FIG. 6), proximity sensor 52 will bealigned with a blind hole 61 drilled into the driven wheel. However,proximity sensors 50, 51 will not be aligned with any hole, and willsense the presence of proximate portions of the adjacent driven wheel.

Thus, the three proximity sensors 50, 51, 52 are mounted on the guard,and are arranged to interact with features on the driven wheel at eachof the five index positions. These features may simply be cooperativearrays of one or more holes at each index position, such that eachproximity sensor may sense or determine the presence or absence ofmaterial facing it at each index position. Since the array of featuresis different at each index positon, the output signals from theproximity sensors may be used to indicate the angular position of thehead relative to the frame at each index position. This arrangement isinexpensive and yet effective, and avoids the high cost of encoders orresolvers that are commonly found on CNC machines.

Thus, this aspect broadly provides a machine tool 20, comprising: aframe 22; a member 21 mounted on the frame for rotation about a memberaxis x₁-x₁; an indexing mechanism 23 acting between the frame and memberfor selectively causing the member to rotate relative to the framesequentially between a plurality of angularly-spaced index positions;and a sensor apparatus 40 for determining the angular position of themember relative to the frame, the sensor apparatus including: a firstplurality of sensors 50, 51, 52 mounted on one of the frame and memberand arranged to face toward the other of the frame and member, thesensors being arranged in a first array; a second plurality of features53, 54, 55, 56, 58, 59, 60, 61 provided in the other of the frame andmember at each index position and arranged to face toward the sensors,the features being arranged in a second array; and means 62 forgenerating a signal from the sensors such that the signal will indicatethe particular index position of the member relative to the frame.

The sensor apparatus may employ proximity sensors (as described above),magnetics sensors, or other types of sensor that do or do not contactthe sensors to the driven gear. The sensor apparatus may also bearranged to directly sense the index position of the head itself.

Improved Head Mount (FIG. 4)

In the known prior art forms of mechanical-type multi-spindle machinetools, the member (or head) typically had outwardly-facinglarge-diameter cylindrical surfaces that were simply journalled inlarge-diameter head openings that had inwardly-facing cylindricalsurfaces that were arranged to face toward the head cylindricalsurfaces. Hence, the head was simply journalled on the frame forrotation about the head axis. However, the radial clearance between thefacing cylindrical surfaces of the head and frame contributed to amachining tolerance, and decreased the accuracy and precision of themachine tool.

In FIG. 4, the present invention is shown as providing bearings,severally indicated at 63, between the head and frame. These bearingsseverally have at least one roller element, such as a roller ball 64,arranged between its inner and outer races. Thus, this arrangementallows for ready rotation of the head relative to the frame, while, atthe same time, eliminating the radial clearance that had existed inprior art designs in which the head was simply journalled on the frame.

Thus, this aspect of the invention provides an improved multi-spindlemachine tool (20), which broadly comprises: a frame (22); a member (21)mounted on the frame for rotation about a member axis (x₁-x₁); anindexing mechanism (25) acting between the frame and member forselectively causing the member to rotate about the member axis relativeto the frame sequentially between a plurality of angularly-spaced indexpositions; a plurality of spindle assemblies (28) mounted on the memberfor rotation therewith, each spindle assembly being mounted for rotationrelative to the member about its own individual spindle assembly axis;and at least one rolling-element (64) acting between the member andframe such that the position of the member relative to the frame may becontrolled at each of the index positions.

Improved Tool Slide (FIGS. 7-9)

Referring now to FIGS. 7-9, an improved tool slide, generally indicatedat 65, is shown as being mounted on the machine frame 22. The tool slideincludes a recirculating ball screw 66 and a linear rail 68. The ballscrew is arranged to be rotated by a motor M mounted on the machineframe. The linear rail has a stationary rail-like portion 69 mounted onthe frame, and has a movable portion 70 guided by the rail-like portionand driven by the ball screw. A tool holder 71 is mounted on the movableportion and is arranged to move a tool 72 toward and away from aworkpiece W. The salient feature of the improved tool slide is that itmay be moved toward and away from the workpiece with substantially-zerobacklash. Thus, movement of the tool is substantially proportional tothe polarity and magnitude of the current supplied to the ball screwmotor so that tool position may be controlled electronically.

The improved tool slide may be operatively mounted on the frame toselectively move the tool in an axial or radial direction relative tothe workpiece, as desired.

Therefore, this aspect of the invention provides an improvedmulti-spindle machine tool (20), which broadly comprises: a frame (22);a member (21) mounted on the frame for rotation about a member axis(x₁-x₁); an indexing mechanism (25) acting between the frame and memberfor causing the member to rotate relative to the frame about the memberaxis sequentially between a plurality of angularly-spaced indexpositions; a plurality of spindle assemblies (28) mounted on the memberfor rotation therewith, each of the spindles being mounted for rotationrelative to the member about its own individual spindle axis; a chuckmounted on each spindle assembly for holding a workpiece; means forcontrollably rotating each of the spindle assemblies independently ofone another at a desired angular speed; a zero-backlash tool slide (65)mounted on the frame and arranged to be controllably moved relative tothe workpiece at each index position; and a tool (72) mounted on theslide for imparting an action to the workpiece (W).

Modifications

The present invention contemplates that many changes and modificationsmay be made. For example, while servomotors and the like are preferred,other types of motors may be substituted therefor. Similarly, theinvention is not limited to use with synchronous belt drives. Othertypes of drives might readily be substituted.

In the preferred form, proximity sensors are used as part of the sensorapparatus. However, other types of sensors, such as magnetic sensors,and the like, might be substituted.

Reference to a Davenport® multi-axis screw machine in the claims isintended to be a limitation on the scope of the claims.

Therefore, while preferred forms of the invention have been shown anddescribed, and several changes and modifications thereof discussed,persons skilled in this art will readily appreciate that variousadditional changes and modifications may be made without departing fromthe spirit of the invention, as defined and differentiated in thefollowing claims.

What is claimed is:
 1. A multi-spindle machine tool, comprising: aframe; a member mounted on said frame for rotation about a member axis;an indexing mechanism acting between said frame and member forselectively causing said member to rotate about said member axisrelative to said frame sequentially between a plurality ofangularly-spaced index positions; a plurality of spindle assembliesmounted on said member for rotation therewith, each spindle assemblybeing mounted for rotation relative to said member about its ownindividual spindle assembly axis; a plurality of motors mounted on saidframe; and a plurality of ring gears mounted on said member and engaginga respective one of said spindle assemblies, each ring gear being drivenby a respective one of said motors; whereby said motors may be operatedindependently of one another to selectively rotate the respectivespindle assemblies relative to said member at the desired rotationalspeeds.
 2. A multi-spindle machine tool as set forth in claim 1 whereinsaid ring gears are spaced axially from one another along said memberaxis.
 3. A multi-spindle machine tool as set forth in claim 1 whereineach of said motors has an output shaft and a driving gear mounted onsaid output shaft, and wherein each driving gear is arranged to rotate arespective one of said ring gears.
 4. A multi-spindle machine tool asset forth in claim 1 wherein said plurality is five.
 5. A multi-spindlemachine tool as set forth in claim 4 wherein said machine tool is aDavenport® automatic screw machine, and said member is a head of saidscrew machine.
 6. A multi-spindle machine tool as set forth in claim 1wherein said indexing mechanism is a Geneva indexing mechanism.
 7. Amachine tool, comprising: a frame; a member mounted on said frame forrotation about a member axis; an indexing mechanism acting between saidframe and member for selectively causing said member to rotate relativeto said frame sequentially between a plurality of angularly-spaced indexpositions; and a sensor apparatus for determining the angular positionof said member relative to said frame, said sensor apparatus including:a first plurality of sensors mounted on one of said frame and member andarranged to face toward the other of said frame and member, said sensorsbeing arranged in a first array; a second plurality of features providedin the other of said frame and member at each index position andarranged to face toward said sensors, said features being arranged in asecond array; and means for generating a signal from said sensors suchthat said signal will indicate the particular index position of saidmember relative to said frame.
 8. A machine tool as set forth in claim 7wherein said second plurality is different from said first plurality atsome of said index positions.
 9. A machine tool as set forth in claim 7wherein said sensors are proximity sensors operatively arranged to sensethe presence or absence of material across the interface between saidfame and member, and wherein said features include at least one holeprovided in the other of said frame and member.
 10. A machine tool asset forth in claim 7 wherein said first array is arranged to face towardsaid second array when said member is in each index position.
 11. Amachine tool as set forth in claim 7 wherein said member is a headhaving a plurality of spindle assemblies mounted thereon, wherein saidhead has a head axis, wherein each spindle assembly has an individualspindle axis, and wherein said spindle assemblies are mounted on saidhead for rotation with said head about said head axis and for rotationrelative to said head about their respective individual spindle axes.12. A machine tool as set forth in claim 11 wherein said machine tool isa Davenport® automatic screw machine.
 13. A multi-spindle machine tool,comprising: a frame; a member mounted on said frame for rotation about amember axis; an indexing mechanism acting between said frame and memberfor selectively causing said member to rotate about said member axisrelative to said frame sequentially between a plurality ofangularly-spaced index positions; a plurality of spindle assembliesmounted on said member for rotation therewith, each spindle assemblybeing mounted for rotation relative to said member about its ownindividual spindle assembly axis; and at least one rolling-elementbearing acting between said member and frame such that the position ofsaid member relative to said frame may be controlled at each of saidindex positions.
 14. A machine tool as set forth in claim 13 whereinsaid machine tool is a Davenport® automatic screw machine, and whereinsaid member is a head of said screw machine.
 15. A multi-spindle machinetool, comprising: a frame; a member mounted on said frame for rotationabout a member axis; an indexing mechanism acting between said frame andmember for causing said member to rotate relative to said frame aboutsaid member axis sequentially between a plurality of angularly-spacedindex positions; a plurality of spindle assemblies mounted on saidmember for rotation therewith, each of said spindles being mounted forrotation relative to said member about its own individual spindle axis;a chuck mounted on each spindle assembly for holding a workpiece; meansfor controllably rotating each of said spindle assemblies sindependently of one another at a desired angular speed; a zero-backlashtool slide mounted on said frame and arranged to be controllably movedrelative to said workpiece at each index position; and a tool mounted onsaid slide for imparting an action to said workpiece.
 16. Amulti-spindle machine tool as set forth in claim 15 wherein said toolslide includes a ball screw.
 17. A multi-spindle machine tool as setforth in claim 15 wherein said tool slide includes a linear rail.
 18. Amulti-axis machine tool as set forth in claim 15 wherein said machinetool is a Davenport® five-spindle automatic screw machine, and whereinsaid member is a head on said screw machine.